They leave the light on...
In 1 John 1:5-10, God declares, through his Spirit and through his servants, that he is light, and in him is no darkness at all.
God speaks truth about himself and about us, but we attempt to talk over him, to speak our own version of truth. Three times John describes the claims of darkness -- our speaking over what God has spoken: "if we say" we walk with God but walk in darkness; "if we say" we have no sin; "if we say" we have not sinned.
The one who follows God by walking in light, faithfully reflecting the glory of God -- 'glowing' with his glory -- will, first, declare God's character as light; second, reject the claims of darkness; and third, revel in exposure to God's light, confessing sin so that we are 'lit up' and rid of darkness. In other words, we speak not what we want to say, but what God has spoken about himself and about us.
As we flee darkness to dwell with God in light, he forgives, cleanses, and washes us in the blood of Jesus Christ.